/* ── Calculator ── */
  .calc-wrap {
    display: flex; gap: 32px; flex-wrap: wrap; margin-bottom: 40px;
  }
  .calc-container {
    background: var(--bg-surface); border: 1px solid var(--border); border-radius: var(--radius-xl);
    padding: 20px; width: 320px; flex-shrink: 0;
    position: sticky; top: 20px; align-self: flex-start;
  }
  .calc-display {
    background: var(--bg-inset); border: 1px solid var(--border); border-radius: var(--radius-md);
    padding: 16px; margin-bottom: 12px; text-align: right; min-height: 70px;
    display: flex; flex-direction: column; justify-content: flex-end;
  }
  .calc-expr { font-size: 13px; color: var(--text-muted); min-height: 18px; word-break: break-all; }
  .calc-result { font-size: 28px; font-weight: 700; color: var(--text-primary); word-break: break-all; }
  .calc-grid {
    display: grid; grid-template-columns: repeat(5, 1fr); gap: 6px;
  }
  .calc-btn {
    padding: 12px 4px; border: none; border-radius: 10px;
    font-family: var(--font); font-size: 13px; font-weight: 600;
    cursor: pointer; transition: all 0.15s; background: var(--bg-inset); color: var(--text-primary);
  }
  .calc-btn:hover { background: var(--border); transform: scale(1.05); }
  .calc-btn:active { transform: scale(0.95); }
  .calc-btn.op { background: var(--concept-bg); color: var(--concept-text); }
  .calc-btn.op:hover { background: var(--concept); color: var(--text-white); }
  .calc-btn.fn { background: var(--example-bg); color: var(--example-text); font-size: 12px; }
  .calc-btn.fn:hover { background: var(--example); color: var(--text-white); }
  .calc-btn.eq { background: linear-gradient(135deg, var(--concept), var(--concept-dark)); color: var(--text-white); }
  .calc-btn.eq:hover { box-shadow: 0 4px 12px rgba(139,92,246,0.4); }
  .calc-btn.ac { background: var(--error-bg); color: var(--error-text); }
  .calc-btn.ac:hover { background: var(--error); color: var(--text-white); }
  .calc-btn.highlight { animation: calcPulse 0.6s ease; }
  @keyframes calcPulse {
    0% { box-shadow: 0 0 0 0 rgba(139,92,246,0.6); }
    50% { box-shadow: 0 0 0 6px rgba(139,92,246,0); }
    100% { box-shadow: none; }
  }

  .calc-guide { flex: 1; min-width: 300px; }
  .guide-card {
    background: var(--bg-surface); border: 1px solid var(--border); border-radius: var(--radius-lg);
    padding: 24px; margin-bottom: 20px; transition: border-color 0.3s;
  }
  .guide-card:hover { border-color: rgba(34,197,94,0.4); }
  .guide-card h4 { color: var(--example); font-size: 16px; margin-bottom: 12px; }
  .guide-card code, .calc-guide code {
    font-family: var(--font);
    background: var(--border); padding: 1px 6px; border-radius: 4px;
    font-size: 14px; color: var(--text-primary); font-weight: 600;
  }
  .guide-card .goal { color: var(--text-secondary); font-size: 14px; margin-bottom: 16px; }
  .step-list { list-style: none; padding: 0; counter-reset: step; }
  .step-list li {
    display: flex; align-items: center; gap: 12px;
    padding: 10px 0; border-bottom: 1px solid var(--border-subtle);
    font-size: 14px; counter-increment: step;
  }
  .step-list li:last-child { border-bottom: none; }
  .step-list li::before {
    content: counter(step);
    display: flex; align-items: center; justify-content: center;
    width: 24px; height: 24px; border-radius: 50%;
    background: var(--concept-bg); color: var(--concept-text);
    font-size: 12px; font-weight: 700; flex-shrink: 0;
  }
  .key-badge {
    display: inline-block; padding: 3px 10px;
    background: var(--border); border: 1px solid #3a3a5c; border-radius: 6px;
    font-family: var(--font); font-size: 13px; color: var(--text-primary); font-weight: 600;
  }
  .key-badge.fn-key { background: var(--example-bg); border-color: var(--example); color: var(--example-text); }
  .key-badge.op-key { background: var(--concept-bg); border-color: var(--concept); color: var(--concept-text); }
  .guide-result {
    margin-top: 12px; padding: 12px 16px;
    background: rgba(34,197,94,0.08); border: 1px solid rgba(34,197,94,0.2);
    border-radius: 10px; font-weight: 700; color: var(--example-text); font-size: 15px;
  }
  .try-btn {
    display: inline-flex; align-items: center; gap: 6px;
    margin-top: 12px; padding: 8px 20px;
    background: linear-gradient(135deg, var(--example), #16a34a); color: var(--text-white);
    border: none; border-radius: 10px; font-family: var(--font);
    font-size: 13px; font-weight: 700; cursor: pointer; transition: all 0.2s;
  }
  .try-btn:hover { transform: translateY(-1px); box-shadow: 0 4px 12px rgba(34,197,94,0.3); }

  @keyframes quizGlow {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(10deg); }
  }